During the fermentation of red wine grape must, a solid cake of pomace builds up and floats on the surface of the fluid. It has been found that the quality of red wine is improved when the juice remains in intimate contact with the pomace for a certain period of time. The required thorough mixing was accomplished heretofore only by having an attendant cut through the pomace cake with a plunger or rake and punch the material down into the body of the juice. This procedure is possible only with open-topped tanks and is, moreover, quite difficult because the fermenting crushed grape mass causes the formation of an extremely dense cake of pomace, called "cap" that floats on the surface of the body of the fluid. Also in the processing of other types of must, as for example white wine grape must, it may be desirable to thoroughly mix all of the must, including the pomace.